Selective removal of volatile substances injected into a chromatographic packing filled column

ABSTRACT

A flow of a carrier gas through a column is provided. A sample is provided in the column, and a temperature of a longitudinally short portion of the column is raised to a predetermined controlled high temperature at which volatile substances are released from the sample packing and are carried by the carrier gas. The column is cooled on each side of the short portion to a low temperature at which the volatile substances condense or adsorb on the column packing. By continuously moving the heated short portion from an inlet end to an outlet end of the packing in a direction of carrier gas flow the volatile substances selected by the controlled high temperature are released. Four particularly useful and advantageous applications can be identified for the invention. Firstly, it provides an improved gas chromatograph (GC) injector. Secondly, it provides an improved thermal separator or extractor. Thirdly, it provides an efficient way to analyze target compounds suspected of being contained within a complex mixture by allowing for the GC analysis to be carried out only on those compounds or substances falling within the same or similar thermal desorption characteristics as those of the target compound. Lastly, by operating in a full time-coupled time-resolved (TCRC) mode, a complete three-dimensional analysis output can be obtained giving better power of separation of the analyzed sample, which is of particular importance when the substance to be analyzed is a complex organic material.

This application is a division of application Ser. No. 07/735,395 filedOct. 15, 1996 now U.S. Pat. No. 5,929,321.

TECHNICAL FIELD

The present invention provides improved separation of chemicalsubstances using chromathermographic techniques. When used inconjunction with a gas chromatograph, the invention further providestime-coupled time-resolved chromatography in which analysis of complexorganic chemical mixtures is improved by providing a first separationaccording to thermal desorption characteristics followed by simplifiedgas chromatography. The invention has application in the areas ofenvironmental analysis, biomedical analysis, drug screening andmetabolism, biotechnologies, fuel analysis and many other areas in whichit is necessary to characterize chemical species which are found incomplex mixtures.

BACKGROUND OF THE INVENTION

In chromatography, a mixture, vaporized in a carrier gas, is introducedinto a column where differential migration of the compounds, through thecolumn, results in their separation. The compounds take different timesto travel the length of the column. Compounds having more affinity forthe packing in the column will tend to be retained in the packing, andtheir migration through the column will take a longer time. However, asthe number of compounds in the mixture increases, it becomes likely thattwo or more compounds will have similar affinities for the packing and,therefore, their migration times will become close to one another oralmost identical. When this occurs, the compounds to not separate, andthey will co-elute from the column. One of the ways that can be used toseparate the co-eluted chemicals is re-injecting the non-separatedcompounds into a second chromatographic column as they elute from thefirst. In this "heart-cutting" technique, the flow of the first columnis diverted into a second column temporarily at the elution time of thenon-separated components. The chromatographic process continues on thesecond column which has a different packing, and separation can beachieved, as shown in FIG. 1. In this technique that uses two gaschromatographs combined in series, the mixture has to be re-injected ifanother "heart-cut" is to be made in order to separate another region ofthe chromatogram.

A second approach that has been proposed produces multidimensionalseparation by modulating the temperature of the chromatographic column.In this arrangement, the sample flows through a first column at a giventemperature, and the column is continuously modulated in temperature atits end. The temperature is cooled so as to temporarily retain compoundsin the flow for a short period of time, and then flash-heated in orderto desorb them into a second column in series with the first. Thus, atperiodic times, the second column analyzes compounds that have beentrapped at the end of the first and acts as a second dimension. Thearrangement is shown in FIG. 2. It is limited in the number of compoundsthat it can ultimately separate because the analysis cycle is short inthe second dimension (=2 seconds). Furthermore, the technique has onlyone mode of operation and cannot be used for the selective and rapidanalysis of one or several target compounds present in a mixture. Thusit seems to be better than conventional chromatography and superior toheart-cutting, since it can expand many regions of a chromatogram usinga single injection of the sample.

In the field of gas chromatography injectors, it is desirable to injectin the gas phase the substances to be analyzed by the gas chromatographas a "short square pulse". The start time of passage through the gaschromatographic separation column should be substantially the same forall of the injected sample to be analyzed. When injecting high volumesof sample, conventional injectors have difficulty releasing thesubstances to be analyzed in an efficient square pulse manner.Furthermore, many complex organic compounds (normally in a solid phaseat room temperature) are preferably injected in solution, only for thesolvent to be discharged at the temperature of the analysis and for theremaining compounds to be released in gas form at the high temperatureof analysis. This known method of injection is limited by the amount ofsolution which can be injected, due to the possible harmful effect onthe gas chromatograph performance caused by a large amount of solventbeing discharged in order to release a satisfactory amount of compoundsfrom the solution. Furthermore, the chromatographic column can besaturated or blocked if too high amounts of compound are injected.

It is an object of the present invention to provide an apparatus forsuperior qualitative analysis of complex chemical mixtures.

It is a further object of the present invention to provide an apparatusand method for the separation and identification of complex chemicalmixtures.

In "Zone Gas Chromatography" by Endre Fuggerth, Analytical Chemistry,Vol. 61, No. 14, Jul. 15, 1989, pp. 1478-1485, there is described anapparatus for selectively removing volatile substances. injected into apacking filled column. The disclosed device has a narrow furnace passingover a column in which a substance to be analyzed is injected. As thefurnace is passed over the zone containing the packing, substancesthermally desorbed are released and carried by a carrier gas passingthrough the column. When the furnace surpasses the packing zone, thesubstances released go into a gas chromatography oven. The ability ofthe disclosed device to efficiently release substances into the gaschromatography (GC) apparatus is limited. Rapid release of the volatilesubstances from the packing filled column into the GC within a shortperiod of time is lost due to the width of the heated zone or area bythe narrow furnace.

It is an object of the present invention to provide an apparatus forsuperior qualitative analysis of complex chemical mixtures.

It is a further object of the present invention to provide an apparatusand method for the separation and identification of complex chemicalmixtures.

It is yet another object of the present invention to provide anapparatus for selectively removing volatile substances injected into apacking filled column in which a very short portion of the column israised to a desired high temperature and swept over the packing torelease volatile substances.

SUMMARY OF THE INVENTION

According to the invention, there is provided an apparatus forselectively removing volatile substances injected into a packing filledcolumn, comprising: a carrier gas inlet provided at one end of thecolumn; a carrier gas outlet provided at an opposite end of the column;mobile heating means able to controllably raise a temperature of alongitudinally short portion of the column for the volatile substancesto be released from the packing and be carried by the carrier gas towardthe outlet; cooling means for cooling the column on each side of theshort portion to a low temperature at which the volatile substancescondense on the packing; and control means for setting a temperature ofthe heating means and for causing the heating means to move over thepacking in a direction of carrier gas flow to release the volatilesubstances selected by the temperature of the heating means.

It has been found that the provision of cooling means such as a watercooled disc or jets of cooling gas provided to cool the column on eachside of the short portion raised by the heating means to the desiredhigh temperature is effective in improving efficiency of the apparatusboth for the purposes of providing an improved GC injector and forproviding a chemical substance extractor for separating substances froma complex mixture of substances according to thermal desorptioncharacteristics. In the case of an injector, the invention provides arelatively large column for containing and storing the substances to beanalyzed. Selective and sudden release of the substances in a narrowsquare pulse is made possible by the heating and cooling means. In thecase that the substances to be analyzed are contained in solution, themost volatile solvent can be initially released and vented withoutpassing into the GC, thus increasing the efficiency of the analysis. Theinjection can be repeated while venting the solvent which allows theinjection volume to be increased. Selective release of some of thecompounds using the heating means into the GC avoids the saturation ofthe GC column. In the case that the substances to be analyzed are insolid, permeable form, it may be possible to insert the solid sampleinto the column for direct removal of the substances to be analyzed bythe GC.

When the apparatus according to the invention is coupled to a GC, theinvention further provides an apparatus for carrying out time-coupledtime-resolved chromatography (TCRC) in which a sample of the substanceto be analyzed is injected into the packing filled column and then theGC analysis is carried out in a plurality of stages related to aplurality of temperatures at which the mobile heating means are operatedto release a portion of the sample, the entirety of the sample beingreleased as the temperature of the heating means is increased to itsmaximum final temperature. The result is that each GC analysis islimited to a fewer number of substances, and therefore, is simplified.By arranging the GC results according to the heating means temperature,the chemical analysis data is given a three-dimensional perspective. Inaccordance with this aspect of the invention, the control meansaccording to the invention comprise means for setting an initial and afinal temperature for the heating means temperature; means fordetermining a temperature increment; cycling means for causing theheating means to repeatedly remove the substances from the packing forrelease into the gas chromatograph beginning at the initial temperatureand ending at the final temperature by the temperature increment; delaymeans for delaying the cycling means to space apart the consecutiverelease of the substances by an amount of time required to preventoverlap of analysis; and means for recording results of the analysis bythe gas chromatograph for each cycle along with the heating meanstemperature for each cycle.

According to the invention, there is also provided a method forselectively removing volatile substances injected into a packing filledcolumn, comprising the steps of:

a) providing a flow of a carrier gas through the column;

b) raising a temperature of a longitudinally short portion of the columnto a predetermined controlled high temperature at which the volatilesubstances are released from the packing and be carried by the carriergas;

c) cooling the column on each side of the short portion to a lowtemperature at which the volatile substances condense or adsorb on thepacking; and

d) continuously moving the heated short portion from an inlet end to anoutlet end of the packing in a direction of carrier gas flow to releasethe volatile substances selected by the controlled high temperature.

Preferably, at least one incomplete pass using the mobile heating meansis carried out, i.e. the short portion of the column raised to thepredetermined controlled high temperature is moved from the upstream endof the packing to a point near the downstream end of the packing so asto leave the volatile substances released at the controlled hightemperature deposited near the downstream end of the packing. Aftercompleting the at least one incomplete pass, a complete pass is carriedout during which the volatile substances are released as a result of theheated short portion passing over the downstream end of the packing. Inthis way, a higher portion of the volatile substances which can bereleased at the predetermined controlled high temperature are releasedinto the outgoing flow of carrier gas.

Four particularly useful and advantageous applications can be identifiedfor the apparatus and method according to the present invention.Firstly, the invention can be used to provide an improved GC injector.Secondly, the invention can be used to provide an improved thermalseparator or extractor. Thirdly, the invention provides an efficient wayto analyze target compounds (Target Compound Analysis or TCA mode)suspected of being contained within a complex mixture by allowing forthe GC analysis to be carried out only on those compounds or substancesfalling within the same or similar thermal desorption characteristics asthose of the target compound. Lastly, by operating in a full TCRC mode,a complete three-dimensional analysis output can be obtained givingbetter power of separation of the analyzed sample, which is ofparticular importance when the substance to be analyzed is a complexorganic material. The latter mode produces a novel type of mapping ofanalytical results that indicates the true complexity of the sample. Ascan be appreciated, the apparatus according to the invention preferablycomprises a vent at the outlet of the column whereby a scan by theheating means releasing substances which are of little analyticalinterest can be discarded before carrying out a subsequent scan at ahigher temperature to release substances of interest which, instead ofbeing vented, are injected into the GC or are collected or otherwisetrapped for subsequent use.

As can also be appreciated, the invention has application in those caseswhere conventional GC fails to resolve between two closely related peaksby providing an accurate way to carry out a plurality of GC analyseswith the sample separated according to thermal desorptioncharacteristic. As can be appreciated, the invention allows theseparation of more components per analysis (five to ten times) thanconventional GC.

When the substance detector provided at the output of the GC is a massspectrometer, a more accurate and positive identification of thesubstance making up each peak in the GC result is provided. Theinvention allows by the use of pattern recognition to merge signalscaused by a single compound eluding in several thermal scans.

BRIEF DESCRIPTION OF THE DRAWINGS

While the novel features of the invention are set forth withparticularity in the appended claims, the invention, both as toorganization and content, will be better understood and appreciated,along with other objects and features thereof, from the followingdetailed description taken in conjunction with the drawings, in which:

FIG. 1 is a graphic representation of the "heart-cutting" technique usedin multidimensional gas chromatography known in the prior art;

FIG. 2 is a schematic depiction of the technique of temperaturemodulation used in multidimensional gas chromatography known in theprior art;

FIG. 3 is a block diagram of the time-coupled time-resolvedchromatography (TCRC) method according to a preferred embodiment;

FIG. 4 is a three-dimensional graphic depiction of the coordinates for acompound;

FIG. 5 is a schematic representation of the TCRC chromatograph;

FIG. 6 is a schematic representation of the thermal zone assembly;

FIG. 7 is a graphic representation of the TCRC device in its gaschromatograph emulation mode;

FIG. 8 is a graphic representation of the TCRC in the target analysismode;

FIG. 9 is a graphic representation of the TCRC device in the fullmapping mode;

FIG. 10 is a graphic representation of the TCRC of a reconstructed mapin the full mapping mode; and

FIG. 11 is a cross-sectional elevation view of the injector columnaccording to the invention;

FIGS. 12 and 13 are a side and top view respectively of an injectorcolumn, four-way valve and cold trap assembly according to theinvention;

FIG. 14 is sectional view of the heating means and cooling means of theembodiment of FIGS. 12 and 13;

FIG. 15 is a schematic view of thermal extraction device according tothe invention; and

FIG. 16 is a more detailed view of the injector illustrated in FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As mentioned above, the present invention has at least four separateapplications. The basic apparatus 20 comprises, as illustrated in FIG.11, a column 25 filed with a stationary phase or packing 26 and glasswool end plugs 26b. A carrier gas inlet 21 provides a source for carriergas flow through the column 25. The outlet 22 is illustrated ascommunicating with a gas chromatograph inlet 42, a vent or trap 28 and asecond carrier gas inlet 44. In the case of a solution to be analyzed orseparated, a needle injector is inserted through septum 24. A septum cap45 is provided. The mobile heating unit 30 comprises an electric ringheater 32 mounted on a positioning motor unit 36. Water cooled rings 33aand 33b are mounted with the heater 32 by a bracket 37, and insulation34a and 34b is provided between the heater 32 and the rings 33. The gapbetween the glass, fused silica or quartz column 25 and the heater 32and cooling rings 33 is less than 50 μm, and preferably the tolerance ofthe diameter of the column is good enough to allow for a very small gap.As illustrated schematically, the motor mounting 36 moves on a racksupport 35. Motor movement and control of the temperature is carried outby control circuit 40. A temperature sensor 38 generates a temperaturereference signal used for temperature control.

A sensor probe 38a is also inserted into the column at the top andextends into the top of the packing 26. This probe 38a is used tocalibrated the internal temperature of the column as a function ofscanning speed. Unit 30 is passed over sensor 38a whenever its speed ortemperature has to be changed. A feedback circuit contained withincircuit 40 ensures that the power input into the heating element 32 issufficient to obtain the desired temperature at the given scan speed.

When a solution or liquid is injected into column 25 through the septum24, adsorption in packing 26 takes place. Such adsorption may take placeover a relatively large volume. As the heated zone sweeps over thepacking 26, volatile substances are thermally desorbed and carried bythe carrier gas towards the outlet 22. As illustrated at 27, aconcentrated band of substances released at the temperature of thepacking raised by the heater 32 can be created by sweeping the mobileheater unit 30 to almost the end of the packing. After completing suchan incomplete sweep, a complete sweep can be carried out and thesubstances can be released into the outlet 22.

As can be seen, in the embodiment illustrated in FIG. 11, a temperaturecontrolled transfer zone 46 is present. The end of column 25 is seatedin a column end fitting 50 communicating with outlet tube 22. A secondcarrier gas inlet 44 is connected via a valve 47 to outlet 22. A purgevalve 48 is also connected to outlet 22 and leads to a vent or cold trapconduit 28. Also connected to outlet 22 is a valve 49 controlling flowfrom the outlet into a gas chromatograph inlet 42.

As illustrated in FIGS. 12 through 14, a different embodiment of theinvention contemplates a horizontal arrangement in which the column 25leads into a four-way valve 60 for connecting the carrier gas flow fromcolumn 25 to either a cold trap 62 or a vent 28. As seen in FIG. 13, adriven pinion gear and rack assembly are used to drive the mobileheating means 30 along the length of column 25. As seen in FIG. 14, thisembodiment contemplates the use of air or CO₂ for cooling the zones oneach side of the heater element 32 by forced convection. As illustratedin FIG. 12, the four-way valve 60 is contained within a heated chamber62 to keep the valve and fittings at a temperature at which adsorptionof the removed substances is prevented. The cold trap 62 comprises acold gas inlet 53 and a cold gas outlet 54, the cold gas inlet 53communicating with a heater tube 55 at its lower end. The heater tube 55has an opening in its upper end for communicating the cooling gas withthe surrounding chamber and the cooling gas outlet 54. The releasedsubstances passing into the heater tube 55 from the four-way valve 60are adsorbed onto the surface of the heater tube 55. Release of theadsorbed materials is achieved by heating electrically tube 55 andallowing the carrier gas flow to transport the substance into the upperend of the gas chromatography capillary column 56.

In the embodiment illustrated in FIGS. 12 and 13, the column isapproximately 50 centimeters long (range of about 10 cm to 150 cm) topermit accurate separation of the materials adsorbed in column 25. Thisembodiment is particularly useful for TCRC and TCA analyses. In theembodiment of FIG. 11, an injector may be provided in which case thecolumn height may be as short as a few centimeters.

As can be appreciated, the heating device 32 could also comprise aradiative element or even a laser source. The motor positioning device36 could also in the case of a laser be replaced by suitable optics tomove the point of radiative energy along the column. The column couldalso comprise a radiation absorbing lining to absorb the radiation andprevent penetration of the radiation to the inside the column. It wouldalso be possible to direct a plurality of cooling gas jets along theentire length of the column. In the case that radiative means are usedto heat the longitudinally short portion of the column, it is alsopossible to provide a cooling jacket on a column through which a coolingfluid would be circulated provided that the jacket and fluid aresubstantially transparent to the heating radiation.

The preferred embodiment of the invention in which a TCRC device isprovided is now described.

The technique of time-coupled time-resolved chromatography (TCRC) is amultidimensional technique that operates in a different way than thosedescribed previously. In order to achieve multidimensional analysis,TCRC uses time coupling of two chromatographic columns physicallycoupled in series. As shown schematically in FIG. 3, the system uses afirst separation stage which consists of a column maintained at lowtemperature (separation stage 1) in which some separation is achieved byscanning a narrow thermal zone alongside the column. This type ofchromatography, called "chromathermography", has been studied previouslyand found to have a low separation power. The thermal zone, as it movesdownwards, will carry compounds with the appropriate volatility down thecolumn into an interface where the compounds are cryogenically trappedand then injected into a second separation stage. The second stage,which consists of a conventional gas chromatograph, then separates thecompounds that have been "extracted" from the first column by thethermal zone. The entire process can be repeated at a higher temperatureof the thermal zone and so on, until all the compounds present on thefirst column have been vaporized, transported into the analyzing systemand separated. Thus, the second chromatograph resolves the components intime, and all the chromatograms that are acquired by repetitive andsubsequent injection of the compounds carried by the thermal zone can betime-coupled. From the entire data set it is possible, as shown in FIG.4, to plot a tridimensional map of the initial mixture in which eachcompound will be characterized by an intensity coordinate and tworetention coordinates (I₁,I₂) corresponding to its retention propertiesin separation stages 1 and 2. If the detection system is a massspectrometer, then the data will be represented in four dimensions, andthis will increase selectivity.

The resulting map of the mixture is the result of the combinedthermal-chromatographic process occurring in stage (I₁), and thechromatographic process occurring in stage 2 (I₂) If, for example, 400compounds can be separated by the chromatograhic process in stage 2(conventional gas chromatograph) and the thermal process in stage 1 hasa temperature resolution of 10° C. for the range 50° C.-300° C., thetotal plane (I₁,I₂) will be able to accommodate 10,000 compounds[((300-50/10)×400]. This technique, thus, offers a very high separationpower, and this makes it of high analytical interest. As will bedescribed further on there are other ways of operating an instrumentbased on TCRC technology.

A typical TCRC chromatograph is shown in FIG. 5. As can be seen from thefigure, the first separation stage consists of an injector (1), a columnoperated at low temperature (ambient) (3) and a narrow thermal zoneassembly (2) that can be scanned alongside the column. The rest of thestage includes a gas line that provides the carrier gas. The first stageis connected to the second stage through a first interface (4) and acold trap (8). The second stage, which is a conventional chromatograph,consists of an interface (5) that is used as an injector, a megabore ora capillary analytical column (6) and a detector (7). Depicted are gasvalves A, B, C, D and E.

Valves A and B, illustrated in FIG. 5, may be used separately as a highperformance injector.

The injector is made of stainless steel. As can be seen in FIG. 5, ithas a gas entrance on the left-hand side and holds the column at thebottom by a `swage-lock` assembly. At the top of the injector, a septumis used in order to inject the sample onto the column with a syringe.The septum allows the system to be air-tight.

The cold column 3 in separation stage 1 is made of quartz or othersimilar materials. It is approximately 50 cm in length and varies from0.5 mm to several mm in diameter. The inside diameter is 0.2 mm or more.The inside of the column is wall coated or packed with a chromatographicstationary phase distributed on particles of varying diameters. Thestationary phase can vary in nature. The primary role of the column isto produce a primary separate of mixture components and freeze theseparation outside the thermal zone assembly.

The scanning thermal zone assembly 3 comprises three elements, as shownin FIG. 6. The element in the center can vary in length from 1-6 mm andcan be heated in between 50-300° C. On each side of the high temperaturezone are placed two zones which are cooled by water or some other means(thermoelectrical device).

This assembly, which allows a square heat pulse to be obtained, isscanned alongside the column by means of a computer-controlled driveassembly. Although there is no limitation to the speed of the zone, ithas to be slow enough so that proper heat transfer to the center of thecolumn can occur efficiently. The temperature of the zone is variablefrom 50-300° C. and is regulated to 0.1° C. The lack of confinement ofthe high temperature zone by cold frontiers results in an inadequateheat profile, especially if the column is mounted vertically. The columncan also be mounted horizontally.

This interface 4 allows the transfer of the compounds contained in thethermal zone to the cold trap. In other modes of operation (targetcompound analysis), the carrier gas exiting the column is allowed to bevented to atmosphere using valve D. The interface 4 is heated (˜300° C.)and contains a spring-loaded device that reduces the effect of the coldzone at the bottom of the thermal assembly 3 on the transfer of thecompounds trapped in the hot zone.

The cryogenic trapping zone 8 is used to condense volatile compoundseluting from the first column during the scan of the thermal assembly 3.Once the scan(s) is terminated, the content of the trap can be injectedin the second stage by flash-heating the trap. There are several ways tocool or flash-heat the trap. The second trap can be flushed at any timeby inputting gas through valve B and venting the gas through valve E.

Interface 5 is used in order to transfer the compounds frozen in thetrap to the second stage of separation after the flash-heating of thetrap. It is used as an injector for the conventional chromatograph usedin the analysis stage. It is usually heated at ≈300° C. and can be usedto vent the trap by opening valve E. It can also be used to input thecarrier gas in the second column through valve C during analysis in thesecond stage. In this fashion, the second stage can be operatedindependently from the first, or scanning in the first section can beconducted concurrently to analysis in the second stage.

The analyzer column 6 resides inside a conventional gas chromatographwhich is operated in an isothermal or temperature programmed mode. Thecolumn can be a capillary or megabore type column. Its role is toseparate the components that have been transported by the scan of thethermal zone and trapped. The temperature cycle of the analyzer columncan be matched with that of the thermal zone assembly. The nature of thestationary phase on this chromatographic column can be different orsimilar to that used in the first column.

The detection system 7 used in TCRC can be any detector that ispresently used in gas chromatography or a mass spectrometer. When a massspectrometer is used (TCRC/MS), the selectivity of the system isincreased tremendously because the technique operates in four dimensionsinstead of three. Other advantages of the mass spectrometer such as itsselected ion monitoring mode, can also be used.

The detection system is interfaced to a data acquisition and treatmentstation that is also used to generate the output of the analysis showingthe components in the mixture. The output map has to be calculated in aspecial way for the data to be reproducible, and this will be discussedin the operation modes below.

The three basic modes of operation are: i) emulation of a gaschromatography ii) target compound analysis and iii) full mixturemapping.

When the system emulates a conventional gas chromatograph, the TCRCinstrument is operated in the following way. The mixture to be analyzedis injected in stage 1 and the thermal zone is scanned down the columnonce or several times, depending on the quantity of compounds present atits maximum temperature (≈300-350° C.). In this way, all the volatilecomponents in the mixture are transported by the thermal zone and theyare simultaneously injected in the second stage. The analyzer column is,thus, temperature programmed from 50° C. to ≈350° C. and produces asingle chromatogram of the mixture in which all the components arepresent.

The chromatogram generated in this operating mode is similar to whatwould be obtained if the mixture was analyzed on a conventionalchromatogram, as shown in FIG. 7, where the top chromatogram wasobtained on a conventional chromatograph and the bottom, on the TCRCinstrument emulating a conventional chromatograph. However, theperformance, in, terms of sensitivity and resolution, can be better(two- to fourfold) on the TCRC instrument because of the bandcompression phenomenon occurring in the first stage.

The second mode of operation of the TCRC instrument is the mode fortarget compound analysis (TCA). This mode allows the rapid and selectiveanalysis of predetermined compounds in a mixture. In this mode, once thetemperature for extracting the compound of interest in the separationstage 1 has been determined, the thermal assembly is scanned just belowthat temperature. With valve D opened to the atmosphere, the scan,containing all the compounds more volatile than the compound ofinterest, is vented. The next scan is conducted at the appropriatetemperature for the compound of interest to be transported by thethermal zone assembly and transmitted to the second stage which willconduct further separation of the compounds eluted in this scan. Sincemost of the more volatile compounds have been eliminated by the firstscan, and the less volatile will have stayed behind at the temperatureof the second scan, it is possible to rapidly analyze the desiredcompound with high sensitivity and selectivity. If other compounds needto be analyzed in the same mixture, then the process can be continued bysuccessively discarding the fractions at a temperature lower than thatof the desired compounds and scanning the thermal assembly at theappropriate temperature for each of the compounds of interest. This scanmode is unique to TCRC and is shown in FIG. 8, where the topchromatogram was obtained on a conventional gas chromatograph, and thecomponent of interest (C₁₅) was selectively analyzed from the mixture bythe TCRC instrument in its target compound mode. This procedure willenable the analyst to save time while maintaining high sensitivity andselectivity in the analysis. The latter mode has many applications inthe field of quality control or environmental control.

The third mode, which is the full mapping mode, is used tosystematically analyze all the components of a mixture. In this mode,the thermal assembly is scanned alongside the first column starting at alow temperature (50° C.) and its content of volatile componentstransferred to the second stage of analysis. Then, the hot zone isincreased in temperature (≈+10° C.) and re-scanned with transfer of itscontent and analysis in the second zone. This process is repetitivelydone until the total temperature range of the thermal assembly has beencovered (≈50-350° C.). At each temperature that the thermal assembly isscanned alongside the first column, a chromatogram is obtained fromstage 2 and these chromatograms are stored in the memory of the dataacquisition system. Each of these chromatograms represents theseparation of components that have been extracted from the mixture at agiven temperature and transported by thermal assembly. It is thereforepossible to map the entire mixture by plotting each of the time-resolvedchromatograms in a time-coupled fashion, as shown in FIG. 9.

In this fashion, all the chromatograms obtained in the second stage willbe from left to right on the retention time axis. By plotting eachchromatogram at the temperature it was obtained from the initialtemperature (T_(i)) to the final temperature (T_(f)), all chromatogramsare now linked together (time-coupled). The third axis is the intensityaxis where the intensities of each peak (not shown) in the chromatogramsare displayed. The map shown in FIG. 9, thus, represents the new datamatrix provided by the technique in the full map scan mode.

Because of variation in several experimental parameters, however, themap shown in FIG. 9 is of limited usefulness because it is difficult toreproduce the raw data. This is due to the fact that the temperature ofthe thermal assembly is jumped and not varied continuously, and that thesame compound may elute out of the first system in two scans rather thanone (two temperatures). A compound which is just not sufficientlyvolatile to be completely eluted by the hot zone at a given temperaturewill partly elute at one temperature, and its elution will be completedin the following scan at a higher temperature. This compound willproduce two peaks in the data set, which is not desirable. Furthermore,the temperature at which a compound elutes is not constant but varieswith column parameters and the speed at which the thermal assembly isscanned. Since in the full map mode, very complex mixtures have to beanalyzed, these uncertainties in the raw data can create seriousdifficulties.

It is possible to eliminate the difficulties mentioned above by usingreference compounds for the system and constructing the map bycalculations. Actually, if instead of using raw retention times one usesindices that convert retention times relative to those of the referencecompounds, and instead of using extraction temperatures, one usesindices converting extraction temperatures relative to those of areference compound, then the calculated map of the mixture can becomeindependent of most experimental parameters and reproducible. In orderto clarify this conversion procedure and explain how a usable map can beobtained, we will describe the conversion procedure for both axes.

The characterization of the compounds eluting from the first stage ofthe system is most difficult and critical since the extractiontemperature can vary with other parameters such as speed of the thermalassembly, and a single compound can elute in two different scans(different temperatures) because its thermal properties do not match thejumps used in the extraction temperatures. Since the temperature of thescans is steadily increased by a constant and arbitrary value, therewill always be a compound that will have a true elution (extraction)temperature in between the values of two scans. For example, if the trueelution temperature of a compound is 58° C., the scan at 50° C. will notbe sufficiently hot to totally elute the compound, which will requirethe next scan at a higher temperature of 60° C. to elute in totality.Therefore, the elution temperature in the first stage of the TCRCinstrument will be calculated as the centroid (T_(e)) of the elutingtemperatures, as shown in the equation below [1]. In the equation, I_(i)refers to the intensities of the peak eluting at temperature T_(i).Thus, if a peak elutes at 20% at a temperature of 50° C. and 80% at atemperature of 60° C., its centroid temperature will be equivalent to58° C. This way of calculating the elution temperature is, therefore,appropriate to the technique and will compensate for the fact that thescanning temperature is jumped instead of being varied continuously.##EQU1## The elution temperature can be converted to the elution time(t_(e)) with the aid of equation [2]. In this equation, I_(i) refers tothe intensities of the peak eluting in scan S_(i) and t is the timerequired for one scan of the thermal assembly. Thus, if a compoundelutes as previously at 20% in the first scan, and at 80% in the secondscan, and the scan time is 1 minute, its apparent elution time will be1.8 minutes. ##EQU2## The second difficulty that occurs is the variationof the elution temperature in the first stage with experimentalconditions. This problem can be solved by using reference compounds tocompensate for this effect. Because the difficulty mainly arises fromvariations in the elating temperature with scan speed the variationswill also be felt by a reference compound. Since the phenomenonoccurring in the first stage can be compared to a distillation,hydrocarbons can be used as reference compounds. If the temperatures ofelution of a series of hydrocarbons (n-alkanes ranging from C₅ -C₄₀) aremeasured in the system, it will always be possible to brake a compoundeluting at temperature T_(e) by two hydrocarbons with elutiontemperatures above (T_(H+1)) and below (T_(H)) the compound. In terms ofelution times, the corresponding values will be t_(e), t_(H+1) andt_(H). It is thus possible to calculate an elution index for thecompound (I_(i)) which will quantify its elution properties relative tothe hydrocarbons, and the index is obtained with equation [3]. In theequation, n represents the number of carbon atoms of the lowerhydrocarbon, while t_(i), t_(H+1) and t_(H) represent the calculatedelution times for the compound and the two hydrocarbons respectively.The index can also be calculated using elution temperatures. ##EQU3##

The situation for the calculation of an index in the second stage issimilar to the first stage. However, in this case, the situation is lesscomplex due to the fact that in the second stage, the analysis isessentially that of a normal chromatogram. In this case, the index willbe calculated from the corrected retention times of the compounds.

    t.sub.Ri.sup.□ =t.sub.Ri -t.sub.m               [ 4]

The corrected retention time (t_(Ri)) for a compound is given byequation [4] where t_(Ri) and t_(m) refer to the measured retention timeand deadtime in the system. By using these corrected retention times itis possible as before to calculate an index for the second stage (I₂₁)based on the retention times of hydrocarbons (n-alkanes), and this canbe done with the use of equation [5] where t_(Ri), t_(H) and t_(H+1),represent the corrected retention times of the compounds and thehydrocarbons below and above it respectively. This second index, likethe first, can be used to characterize the retention properties of theanalytes in the second system and allow, with the first index, theconstruction of the map of the mixture. ##EQU4##

An example of the results obtained in the full mapping mode is presentedin FIG. 10, where several compounds have been injected and the resultingTCRC map calculated in the fashion specified. The map is constructed bygiving an index of 100 units per carbon atom number for the alkanes sothat the range in indices I₁ and I₂ is from 0 to 4500 representingalkanes up to 45 carbon atoms which are volatile within the workingtemperature range. Because of the way the reference system is chosen,the median line in the map represents a line along which all then-alkanes are aligned. The other compounds appear as points in the planeeach having two coordinates (I₁,I₂). The intensities of the peaks are inthe third dimension which is not shown on the map of FIG. 10. One of theways to represent these intensities is to project the sum of all theintensities found in the I₁ axis on the I₂ axis, and project the sum ofall the intensities found in the I₂ axis on the I₁ axis, thus,generating two visual chromatograms, one on the I₁ axis and one on theI₂ axis, on which the intensities would appear as normalized values.This representation would allow to see where each of the peaks in themap stands relative to the mixture (plane) but also relative to thebands eluting in the first or second separation stage.

An analytical feature of this mapping system which is unique to thistechnique is its ability to give an overall view of the components ofthe mixture, which can be used to follow a situation or indicate thepresence of homologous compounds without the necessity of identifyingall the components present in the mixture.

Because of the reference system used, homologous compounds (thosebelonging to a chemical family) will appear as patterns in the map. Thiscan be seen from FIG. 10, where the four black squares appear as a linein the data plane. Those four compounds are esters cf fatty acidsranging from C₁₉ to C₂₃. The other three compounds present in the mapare not related to the esters, and therefore appear in a random fashion.Hence, because of this reconstructed map of the mixture, not only arethe data reproducible in this format, but additional and uniqueinformation can be obtained from the data.

The three operation modes that have been described for the TCRCtechnique have many analytical applications in chemical analysis andeach of the modes, except for the GC emulation mode, provides newmethods of analysis that allow unique data to be obtained. Most of theobvious applications in the areas of chemical analysis are known to us,and it can be predicted that TCRC or TCRC/MS has an enormous potentialas a new analytical technique. The unique assembled techniques of thepresent invention yield results that cannot be obtained by othertechniques, and represent an entirely new way of looking at a sample.

The principle that is used in the mobile zone thermal extractor is basedon the difference in volatility between various components in a mixtureand also on varying affinities of these components for a givenadsorbant. If a mixture containing several relatively involatilecompounds is deposited in a column containing a stationary phase orpacking (adsorbant) and the column is maintained at ambient temperature,the compounds will remain mostly in the stationary phase. Thepartitioning of each compound between the gas phase and the stationaryphase will be given by equations [6] and [6] where C_(g) and C_(s)represent the concentration in the gas phase and the stationary phaseand C₀ is the total concentration.

    C.sub.g =C.sub.0 (1/1+k')                                  [6]

    C.sub.s =C.sub.0 (k'/1+k')                                 [7]

As can be seen from the equations if the capacity ratio k' (affinity forthe stationary phase) is high which is the case at low temperature thenC_(g) will be small and C_(s) will be large demonstrating that most ofthe compounds will be in the stationary phase where they are nottransported by the carrier gas passing in the column with a velocityv_(C). However, if a concentric narrow high temperature zone bordered bytwo cold zones producing a square heat wave is passed alongside thecolumn the high temperature will cause a significant decrease in k' andthe compounds will tend to pass into the gas phase as shown by equation[6] and [7] since C_(g) will increase and C_(s) will decrease.

Thus, the more volatile compounds will be carried through the column bythe carrier gas if its velocity v_(C) is greater than that of thethermal assembly v_(F).

Assuming that the capacity ratio k' for compound 1 is zero at thetemperature of the zone than C_(g) will be equal to C₀ for this compoundand it will be entirely transported by the gas pocket contained in thethermal zone assembly and it will elute from the column. Compound 2which is less volatile will migrate partly and compound 3 which is notvolatile will essentially not migrate and stay at the beginning of thecolumn. Hence, it has been possible in the given example to isolate orthermally extract compound 1 from the mixture.

In a similar way, assuming that compound 2 was the compound of interest,it would be possible to make a second scan of the thermal zone assemblyat a slightly higher temperature and to elute compound 2 while compound3 which is much less volatile will migrate somewhat but will not elute.In the latter case the first run would have been vented in order toeliminate compound 1 and the second run would have used a trappingdevice in order to collect compound 2. Therefore, whatever the relativevolatility of a compound in a mixture may be, it will always be possibleby the use of the appropriate temperature and scan sequence to isolateit (with varying purity) from the other components having differentvolatility or capacity ratio (k'). If the compound to be extracted isknown, it is possible to use it as a standard to calibrate the operatingconditions for its isolation. If the compound is not known, theoperating conditions can be obtained from knowledge of itschromatographic behavior using a conventional chromatograph.

A typical assembly for the moving zone thermal extractor is depicted inFIG. 5. The carrier gas (Helium) is introduced in the system by openingvalve A which is connected to the injector. The sample is introduced inthe injector using a syringe through a septum or another injectiondevice and the mixture is deposited on the packed column. The column canhave different diameters or lengths depending on the application and theamount of compound to be isolated.

Typically the length would vary between 50 and 200 cm and the diameterfrom 1 mm to several centimeters. The thermal zone temperature whichincludes a hot zone of varying temperature (≈20-400° C.) between twocold zones (water cooled or by forced convection or thermoelectrically)is set to a value below the elution temperature of the compound ofinterest and is passed over the mixture and scanned alongside thecolumn. In order to eliminate the more volatile materials, valve B isopened and valve C is closed. This configuration will force the gas andthe compounds carried by the thermal zone out through B. One or morescans can be performed in this configuration depending on theapplication and the temperature used. Then, the temperature of the zoneis set to the elution temperature of the compound of interest and thezone is scanned closing valve B and opening valve C. This will force thecompound in a trapping device where it can be collected using severalmeans depending on the particular experiment being conducted.

For example, one can use a cold trap in order to collect the compound ofinterest. Conditions in the transfer interface which is used to vent orcollect the sample eluted by the thermal zone can vary. For each type ofapplication the temperature of the thermal zone, the flow of the carriergas, the velocity of the mobile zone, the nature of the stationary phaseand the number of scans performed are all variables that have to beoptimized.

A more detailed diagram which explains the general operation of athermal extractor is shown in FIG. 15. With this arrangement, a solidsample (or a liquid on a substrate) is placed in a cartridge andsubmitted to the thermal extraction process and purification through thecolumn. By selecting the valve position, compounds may either bediscarded or sent to a collection zone. Splitting the gas flow beforethis zone allows the gas chromatographic analysis of the collectedfraction.

While specific embodiments of the invention have been illustrated anddescribed herein, it is realized that numerous modifications and changeswill occur to those skilled in the art. It is therefore to be understoodthat the appended claims are intended to cover all such modificationsand changes as fall within the true spirit and scope of the invention.

I claim:
 1. A method for analyzing complex mixtures of organic chemicalcompounds comprising the steps of:a) separating said compounds using achromathermography separation apparatus operating at a controlledtemperature; b) coupling an output of said chromathermography apparatusto an input of a gas chromatography apparatus; c) repeating steps (a)and (b) at at least one other temperature to obtain a plurality of gaschromatograph output traces at neighboring ones of said controlledtemperatures; and d) determining a quantity of at least one of saidcompounds in said mixture by analyzing at least two of said plurality oftraces, wherein said analyzing comprises identifying a quantity of saidat least one of said compounds in said mixture from each of said atleast two of said plurality of traces, and said determining comprisescombining said quanitity identified from each of said at least twotraces.
 2. A method in accordance with claim 1, wherein saidchromathermography apparatus is connected to said chromatographyapparatus by a zone containing a first interface and a cryogenictrapping zone, wherein compounds extracted from said chromathermographyapparatus are trapped in said cryogenic trapping zone prior to beingreleased into said chromatography apparatus.
 3. A method according toclaim 2, wherein said scanning of said thermal zone is repeated untilall compounds present in said chromathermography apparatus have beenvaporized, trapped in said cryogenic trapping zone, transported intosaid chromatography apparatus and separated.
 4. A method according toclaim 1, wherein said chromathermography apparatus comprises a firstcolumn maintained at low ambient temperature wherein separation isachieved by scanning a narrow thermal zone alongside the column.
 5. Amethod in accordance with claim 1, wherein said chromathermographyapparatus comprises a first injector, a column operated at lowtemperature, and a narrow thermal zone assembly that can be scannedalongside said column.
 6. A method in accordance with claim 5, whereinsaid chromathermography apparatus further includes a gas line thatprovides a carrier gas for said complex mixtures.
 7. A method inaccordance with claim 1, wherein said chromatography apparatus comprisesa second injector, an analytical column and a detector.
 8. A method inaccordance with claim 7, wherein said analytical column is aconventional megabore column or a capillary column.
 9. A method inaccordance with claim 7, wherein said detector is a mass spectrometer,wherein said traces are two-dimensional traces.
 10. A method inaccordance with claim 9, wherein hydrocarbons are used as referencepoints in order to eliminate experimental variations, and calculateretention indices I1, I2.
 11. A method in accordance with claim 7,wherein said second injector is an interface.
 12. A method for analyzingcomplex mixtures of organic chemical compounds, comprising the stepsof:a) scanning a thermal zone assembly over a first column at a firsthigh temperature, vaporizing and separating all compounds in said firstcolumn which are released at said first temperature; b) venting saidcompounds released at said first temperature; c) scanning said thermalzone assembly over said first column at a second high temperature tovaporize and separate at least one target compound; d) transporting saidvaporized target compounds in said first column into a second separationstage; and e) analyzing said vaporized target compounds.
 13. A methodfor analyzing complex mixtures of organic chemicals, in accordance withclaim 12, wherein said steps (c), (d) and (e) are repeated at leastonce, resulting in sequential vaporization of all compounds present insaid first column.